1. Field of the Invention
The invention relates generally to a process for making shaped articles from a base polymer containing additives, and in particular to a process for adding a polyester polymer to a pigmented polyamide base polymer and spinning the polymer mixture into a multifilament yarn.
2. Description of the Prior Art
Pigmented polyamide yarns have been commercially available for many years.
Pigments are added to molten polyamide base polymer, either directly or as dispersed in a polymeric carrier material. The polymeric carrier material facilitates the distribution of the pigment in the polyamide polymer. Carriers commonly used with nylon 6,6 base polymer include nylon 6 and 6/6,6/6,10 terpolymer. In general, the melting temperature of the polymeric carrier should be lower than that of the base polymer. The pigment dispersed in carrier material is blended with the base polyamide, melted in an extruder and processed into a shaped article. In the finished article, the polymeric carrier material remains "bound" to the pigment particles; that is, the polymeric carrier material remains intimately associated with the pigment particles, and is not detectable as a "free," separate entity, "unbound" from pigment particles. Such yarns have found particular suitability as carpet yarns, allowing carpets to be produced without the need for dyeing. Furthermore, the yarn color is inherent in the polymer, making the yarn more resistant to light and the effects of chemical treatments than dyed nylon yarns.
One disadvantage of spinning fiber from pigmented polymer is that some pigments make the polymer difficult to spin. These difficult-to-spin pigments include Phthalo Green, Phthalo Blue, Channel Black, Antimony Chrome Titanate, Anthraquinone, Perylene Red, Cobalt Blue, Lamp Black, Carbozol Violet, Quinacridone, Indanthrone Blue and blends thereof. These pigments can agglomerate resulting in spinning breaks, or act as nucleating agents resulting in rapid crystallization of polyamide and thus high draw tension and spinning breaks. Some of these pigment particles are abrasive or large enough to cause spinning breaks. Other related spinning problems are poor draw before hot rolls, excessive yarn wraps on feed roll and broken filaments.
It is known to combine polyester and polyamide polymers and spin the polymer mixture into a multifilament yarn. U.S. Pat. No. 3,549,741 (Caison et al.) is representative of such a process. This patent discloses the making of a carpet yarn from a polymer mixture containing a polyamide base polymer and ten percent (10%) to forty percent (40%) by weight polyester based on the weight of the polymer mixture. The polymer mixture may optionally include various additives, including inorganic and organic pigments. In the yarn produced by this process, the polyester may be detected as a "free," separate entity, "unbound" from pigment particles.
The process described in the Caison et al. patent requires certain non-conventional nylon spinning components, namely, an unusually large spinneret capillary cross-sectional area (in excess of 7.times.10.sup.-4 square inches) and a level of attenuation of the filaments that is considerably above normal (70 to 120 versus 40 to 50). The increased level of attenuation of the filaments is accomplished by the combined effects of capillary size, attenuation of the molten filament and drawing of the solidified filament. Such large spinneret capillary sizes and such increased level of attenuation distinguish the process of Caison et al. from a conventional nylon melt-spinning process.
In view of the foregoing, it is believed desirable to spin nylon yarn from polymer having difficult-to-spin pigments therein with an acceptable level of spinning breaks and broken filaments. Furthermore, it is believed desirable for such a process to use conventional nylon melt-spinning techniques.